The eldest son of the Old Took, Isengrim's rule was noticeably short. He was already near his nineties when he became Thain, and died ten years later. As he had no children of his own, his brother Isumbras became the new Thain.[1]

"Isengrim" is of Anglo-Saxon origin and comes from isen meaning "iron" and grim meaning "fierce".

It is likely Isengrim is named after an earlier Isengrim, but it is notable that "Isengrim" is the name of a wolf who appears in many medieval epics, including the story of Reynard the Fox which originated in French folklore.[2]